1. Field of the Invention
The present invention relates to a lock mechanism for a stage apparatus which locks a movable stage when the movable stage, which is freely movable along a specific plane, is in a non-operational state.
2. Description of the Prior Art
A first example of the aforementioned conventional lock mechanism for a movable stage is disclosed in a third embodiment of Japanese Patent No. 3431020.
In this lock mechanism, an image pickup device is mounted to a front surface of the movable stage which is an element of the stage apparatus, and the movable stage is provided on the back surface thereof with an engaging recess (lock hole). An engaging member (lock pin) which is freely movable forward and reverse in directions parallel to an optical axis is installed behind the stage apparatus (the movable stage), and the movable stage which is in a non-operational state in which no hand-shake correction is performed is locked by engaging the engaging member with the engaging recess.
A second example of the aforementioned conventional lock mechanism for a movable stage is disclosed in a first embodiment of Japanese Patent No. 3431020.
This lock mechanism is provided with one cylindrical boss which projects from the back surface of the movable stage, and first and second abutting members positioned behind the movable stage on mutually opposing sides of the cylindrical boss. The first and second abutting members are linearly movable in a direction parallel to the movable stage.
Upon the movable stage entering a non-operational state in which no hand-shake correction is performed, the first abutting member and the second abutting member move to their respective locked positions where the first abutting member and the second abutting member are positioned closely to each other. Thereupon, approximately half-circle shaped engaging recesses that are respectively formed on opposing surfaces of the first and second abutting members clasp the cylindrical boss. Consequently, the movable stage is locked by the first and second abutting members.
In the aforementioned first example of the conventional lock mechanism, the engaging member (lock pin) is greater in diameter than the engaging recess (lock hole), and the end of the engaging member is conical in shape. When the movable stage is locked, the conical end of the engaging member is engaged in the engaging recess.
However, since the end of the engaging member is conical in shape, there is a possibility of the engaging member moving in a direction to be disengaged from the engaging recess to thereby release the lock unexpectedly if the movable stage slides by a strong force.
Additionally, another problem arises if the lock mechanism disclosed in Japanese Patent No. 3431020 is applied to a hand-shake correction apparatus (image-shake correction apparatus/image-shake reduction apparatus) capable of correcting rotational shake. In this particular type of hand-shake correction apparatus, the movable stage is rotatable for correction of rotational shake. However, even if the engaging member is engaged in the engaging recess, the movable stage cannot be locked to be prevented from rotating because the lock mechanism is provided with only one engaging recess and corresponding one engaging member.
If a lock mechanism like the above described lock mechanism is installed behind the stage apparatus in a manner similar to that in the aforementioned second example of the conventional lock mechanism, the size of the stage apparatus in the optical axis direction increases, which consequently increases the thickness of the stage apparatus in an optical axis direction of a camera in which the stage apparatus is incorporated.
Additionally, providing the movable stage with the aforementioned boss (pin) makes it more difficult to control movements of the movable stage due to the additional weight of the boss, thus making it impossible to perform the hand-shake correction operation with precision.
Furthermore, since the aforementioned second example of the conventional lock mechanism also has only one boss (pin), the movable stage cannot be locked to be prevented from rotating even if the boss is clasped by the first and second abutting members therebetween.